1. FIELD OF THE INVENTION
The field of art to which the claimed invention pertains is processes useful for treating sour petroleum distillates. More specifically, the claimed invention relates to catalytic processes especially useful for the treatment of sour petroleum distillates to effect the oxidation of mercaptans in the distillate to disulfides.
2. DESCRIPTION OF THE PRIOR ART
Processes for the treatment of sour petroleum distillates wherein the distillate is treated in contact with an oxidation catalyst in the presence of an oxidizing agent at alkaline reaction conditions have become well-known and widely practiced in the petroleum refining industry. Said processes are typically designed to effect the oxidation of offensive mercaptans contained in a sour petroleum distillate with the formation of innocuous disulfides--a process commonly referred to as sweetening. The oxidizing agent is most often air. Gasoline, including natural, straight run and cracked gasolines, is the most frequently treated sour petroleum distillate. Other sour petroleum distillates include the normally gaseous petroleum fraction as well as naphtha, kerosene, jet fuel, fuel oil, lube oil, and the like.
A commonly used continuous process for treating sour petroleum distillates entails treating the distillate in contact with a metal phthalocyanine catalyst dispersed in an aqueous caustic solution to yield a doctor sweet product. The sour distillate and the catalyst containing aqueous caustic solution provide a liquid-liquid system wherein mercaptans are converted to disulfides at the interface of the immiscible solutions in the presence of an oxidizing agent--usually air. Sour petroleum distillates containing more difficultly oxidizable mercaptans are more effectively treated in contact with a metal chelate catalyst disposed on a high surface area adsorptive support--usually a metal phthalocyanine on an activated charcoal. The distillate is treated in contact with the supported metal chelate catalyst at oxidation conditions in the presence of an alkaline agent. One such process is described in U.S. Pat. No. 2,988,500. The oxidizing agent is most often air admixed with the distillate to be treated, and the alkaline agent is most often an aqueous caustic solution charged continuously to the process or intermittently as required to maintain the catalyst in the caustic-wetted state.
Heretofore, the practice of catalytically treating mercaptan-containing sour petroleum distillates has involved the introduction of alkaline agents, usually sodium hydroxide, into the sour petroleum distillate prior to or during the treating operation. (U.S. Pat. No. 3,108,081, U.S. Pat. No. 4,156,641). The prior art also suggests the addition to the petroleum distillate along with certain alkaline agents of certain non-alkaline additives. (U.S. Pat. No. 4,124,493, U.S. Pat. No. 4,033,860). In addition, the prior art suggests the use in an alkaline environment of certain catalytic composites produced from metal phthalocyanine solutions containing certain non-alkaline additives. (U.S. Pat. No. 4,087,378, U.S. Pat. No. 4,124,531). The prior art suggests the use of certain chemicals including sodium hydroxide, to increase the solubility of metal phthalocyanine in aqueous solutions from which metal phthalocyanine catalysts to be used in alkaline environments are made. (U.S. Pat. No. 3,108,081). Finally, the prior art shows that an alkali metal hydroxide disposed on an adsorbent support with a metal chelate may be used to treat a sour petroleum distillate without the use of an alkaline agent during treating. The prior art does not disclose or suggest the treating of a mercaptan-containing sour petroleum distillate by contacting the distillate at oxidation conditions with an oxidizing agent and a catalytic composite comprising a metal chelate, an alkali metal hydroxide, and a quaternary ammonium hydroxide, disposed on an adsorptive support. The method of this invention can be used with or without the necessity of addition of an alkaline agent. The consequent savings in materials handling and storage expenses, and avoidance of use of hazardous alkaline chemicals in the treating process, have been long desired.